The technology to transmit electrical signals over a wire onto paper is believed to have been first developed by Alexander Bain, as disclosed in a patent issued to Bain in 1842. This technology has been used by newspapers to transmit text and photographs for many decades. However, facsimile or "fax" technology has been made available to, and used generally by, the public only since the 1960s, when the CCITT convened and subsequently agreed on a series of fax transmission standards, now called Group 1, Group 2, Group 3 and Group 4.
The earliest of the Group 1 fax machines operated as much as a 300 bit per second modem would operate and required six minutes to send a single page. Group 2 fax machines, introduced in the mid-1970s, improved the resolution and cut transmission time to about three minutes per page.
In 1980, the CCITT approved a Group 3 standard, which calls for transmission at up to 9600 bits per second and uses digital image scanning and data compression methods to achieve these high rates. The nominal resolution for a Group 3 fax machine is 200 dots per inch ("dpi"), and a typical transmitted page in normal resolution (203 dpi.times.98 dpi) requires 15-20 seconds to transmit on an uncluttered telephone line. If the page is transmitted in the "fine" mode, the resolution increases to 203 dpi.times.196 dpi and the time required to transmit a page approximately doubles. If the fax machine has built-in gray scale processing capability, the transmission time per page increases approximately exponentially with the number of bits used for gray scale processing. The Group 4 facsimile standard, approved by the CCITT in January 1988, requires use of a leased or other error-free telephone line or of an integrated services digital network ("ISDN"). Transmission rates of up to thirty pages per minute at up to 400 dpi resolution are available with the Group 4 standard.
In 1966, Magnavox developed the first acoustically coupled facsimile machine, the Magnafax 840, which was marketed for business and office applications. This machine used a Group 1 standard and transmitted all the information on an 8.5.times.11 inch sheet in about six minutes.
Multiplex transmission of facsimile signals and television images is disclosed by Beans in U.S. Pat. No. 2,874,213, using the television vertical blanking interval to transmit the facsimile information. A similar approach is disclosed by Weinstein et al. in U.S. Pat. No. 3,491,199 and by Eguchi et al. in U.S. Pat. No. 3,726,992. Krauss et al., in U.S. Pat. No. 3,553,367, discloses multiplexing of two different facsimile signals using amplitude modulation and phase modulation alternatingly to modulate an audio frequency carrier signal.
Other workers have developed special purpose facsimile systems. Kurosawa et al., in U.S. Pat. No. 3,813,483, discloses a facsimile system that uses two scanners to simultaneously scan a pair of parallel bands across a sheet to be transmitted. The two information streams from these two scanners are each used to modulate a carrier signal, with one carrier signal being shifted 90 degrees in phase relative to the other carrier signal, and the two modulated signals are combined in a mixer and sent through a signal line such as a telephone line. The process is reversed at the other end in order to demodulate and restore the original two signals, which are used to reproduce the page of information scanned at the transmitting end.
In U.S. Pat. No. 4,086,620, Bowen et al. discloses the use of a digital signal processor that permutes a stream of image pixel values to increase the run length (maximum length of consecutive black or consecutive white spaces in a line) to increase the efficiency of run length encoding of messages.
Facsimile relay systems that use store-and-forward for error monitoring at the source facsimile station or for conventional relay purposes are disclosed by Oheki in U.S. Pat. No. 4,586,086 and by Kurokawa in U.S. Pat. No. 4,607,289.
Use of buffer memories to receive and temporarily store facsimile signals for data compression and de-compression, television image reproduction and similar purposes are disclosed in U.S. Pat. No. 4,651,221 issued to Yamaguchi, in U.S. Pat. No. 4,663,671 issued to Seto, and in U.S. Pat. No. 4,775,893 issued to Ishikawa.
Furchtgott et al., in U.S. Pat. No. 4,727,538, discloses use of a processor, and a co-processor, together with a data buffer, to allow transmission of data stored in the buffer or, alternatively, transmission of data read directly from memory. Use of a co-processor to run software independently of software being run in the host processor and loadable by the host processor, is disclosed by Irwin in U.S. Pat. No. 4,695,945.
Paneth et al., in U.S. Pat. No. 4,675,863, disclose provision of a plurality of speech channels, data channels or facsimile channels for transmission of signals over telephone lines. Different channels in a telephone trunk line may be used by different subscribers.
In U.S. Pat. No. 4,796,091, Nohtomi discloses a facsimile system that includes a communications terminal, a modem, a memory to temporarily store information that has been received and demodulated by the modem, a display unit to temporarily and selectively display information received, and a recording module to selectively record information received by the terminal. Information received by the terminal is automatically stored in the memory and is then confirmed by the visual display module as required. If any portion of the information received is to be recorded for permanent retention, the recording module is activated and information recording proceeds as required. The modem, memory, display module and recording module appear to operate in a serial manner under the control of a macrocomputer master processing unit ("MPU").
Sfarti et al. disclose use of a plurality of co-processors, operating in parallel and having a plurality of execution modes, in U.S. Pat. No. 4,809,169. The co-processor array requires little, if any, managerial support from the host processor other than activation of each co-processor at appropriate times to perform that co-processor's designated task. The system implements a priority scheme to coordinate execution of the various co-processor tasks.
Each of these systems appears to use a single processor or an array of processors to control transmission, receipt and processing of information through a single signal transmission line. What is needed is a system that allows transmission, receipt and processing of information on each of a plurality of signal-carrying channels at high transfer rates and with the best available resolution.